Water Vapor Feedback

In response to an inquiry to Scott Saleska, Dan Kirk-Davidoff, a prominent expert in the field, has sent the following suggestions:

Soden and Held 2006, An Assessment of Climate Feedbacks in Coupled Ocean—Atmosphere Models, J. Climate 19:3354, DOI: 10.1175/JCLI3799.1 reviews the relative role of various feedbacks in the IPCC AR4 runs.

Held and Soden, “Water Vapor Feedback and Global Warming” Annu. Rev. Energy Environ. 2000. 25:441—75 is a general review of the problem, including discussions of the different dynamics and physics involved in water vapor response to temperature changes in the boundary layer and free troposphere, as well as a discussion of the feedback on a global level. If you haven’t read it, I think you will find it very interesting and though-provoking.

Held and Soden 2000 is online here . Soden and Held was discussed last year in passing. What surprised me in the discussion was that Held’s expectation was that cloud feedback in the GCMs would be positive in some models and negative in others. He expressed surprise in a realclimate comment that it turned out that it was strongly positive in all models. [link] I must say that his surprise intrigued me.

Dan has sent in the following additional reference on convection and cloud modeling:

The problem has been a lack of detailed data. If you could accurately and precisely measure the temperature, water vapor content and cloud radiative forcing over the whole atmosphere at high space and time resolutions, you could go a long way towards testing and correcting the cloud and convection parameterization. Those data are finally becoming available; between the COSMIC GPS satellite network, which can produce accurate temperature profiles through most of the depth of the atmosphere 2500 times/daily, the various spectrally-resolved IR observing instruments (AIRS, IASI, eventually CrIS), and cloud-observing satellites like CloudSat, we are amassing data that will provide a serious capability to falsify model statistics at a wide range of time and space scales.

This is not to say that people haven’t been working on the problem with the data at hand. The ARM observation sites were designed expressly for this purpose- here’s a brief summary white paper on the topic:

The entire issue of water vapor feedback is very important in forming a view on whether increased CO2 content is a big or little problem. Both water vapor feedback and clouds have been identified as critical issues since at least as early as the Charney Report in 1979 and I suspect that much of the difficulty in making much (any) progress in reducing the uncertainties in climate models relates to the difficulty in reducing uncertainty in this area. If one were managing climate model engineering in the same way as space station engineering, I would really focus on this area. Given the sensitivity of GCM results to varying assumptions and parameterizations in this area, I would have liked it if AR4 had devoted entire chapters to each major issue in clouds and water vapor feedback, instead of a few cursory pages.

98 Comments

High and certain mid level clouds constitute time dependent positive feedbacks (function of time of day) – namely, they constitute such a feedback at night and less so or neutral during the day. Net of it is, overall slight postive feedback.

Certain mid and all low level clouds constitute time dependeng negative feedbacks (also TOD function) – namely, they constitute such a feedback during day and less so or neutral at night, with the following caveat. If such clouds are dropping precip, they are an outright negative feedback, with no regard for time of day.

I am wondering how the satellites and other instruments can resolve this issue other than over some relatively long time period. Looking at feedback on a regional scale may not be the same as looking at it globally (just as a possibility). Can anyone here discuss whether local cloud feedback studies can be generalized to the whole globe?

If not, then it may take many years to resolve this. And of course, the satellites have indicated that the globe has not warmed in the last nine years.

RE: #1 – I’d add the following. Whereas, condensation is a exothermic phase change process, the formation of precipitate from droplets of consensate is a process having to do with collisions of droplets, with major influence exerted by attrative and repulsive forces of the droplets, combined with impacts of particulates, various ions, EM energy, and a number of other factors. Falling precipitate is also a process warranting further energetics study.

O.K., perfect place to repost this question: Why are July temperatures in Gulf Coast and Southern states (very high humidity) lower than those at low elevations in the Desert Southwest where humidity is extremely low (same latitude and TOA solar radiation, almost same altitudes). Temperatures are about 3 degrees C higher at low elevation, low humidity Southwest locations. Perhaps you can add a degree for lapse rate. If there is a forcing effect, it appears to me that it is negative. The water vapor decreases the diurnal variation, so that there is more total heat in the air in the South, but not more temperature. (I’m talking about thirty year averages here.)

RE: #4 – Don’t know if these facts answer the question. During summer, the US SW (including a fair bit of the adjacent Pacific) is capped off by the semi persistent Pacific High. On top of that, to its NE there are progressive ridges moving through. The result is a compressive regime and of course, this means hot dry air at the surface for all areas except those where the extreme thermal gradient between the hot land and the cold Pacific results in onshore flow / marine layer / coastal stratus.

On / near the Gulf of Mexico, it’s a different situation entirely. There, a combination of the following is experienced. Midlatitude cyclonic systems brush the area with their southern edges. Simultaneous, tropical systems, e.g. easterly waves, pass through from E to W. And finally, although the Gulf waters are considerably warmer than the Pacific, still, during day, there is enough of a thermal gradient for a very warm and moist sea breeze (contrast this with the Pacific sea breeze, which, even at its saturated Daly City drizzly foggiest, still has lower absolute humidity than a Mississippi sea breeze). Every late afternoon and evening, just inland from the Gulf coast, no matter what the synoptics are doing, as the diurnal atmospheric cooling hits, so too do the thunderstorms. I’ve seen some surface maps which actually depict the so called “sea breeze line” as a front! Add all these factors up, and you just can’t get the air up to 110 degrees in Mississippi most days. Whereas, the factors I mentioned above mean that anywhere in the US SW not affected by the coastal marine layer are very, very hot, when the sun angle is higher than a certain value and high pressure is in control.

Perhaps you should put into context how important feedback is to the big picture of this debate. I remember hearing that the “consensus” was that the average temperature would only increase by 1C for a doubling of CO2 if there were no feedback. Therefore, the 2 to 5 degree predictions require a 200% and 500% feedback respectively.

5. Steve S. I don’t know, either. But for whatever reason sensitivity to increases in radiation are higher in the desert SW than for all areas East of the Rocky Mountains. Obviously, there is a water vapor feedback, or there would be no greenhouse effect at all. However, it seem as if there is some type of threshold water vapor feedback, beyond which no more occurs. Maybe when it becomes sufficiently high, the parasitic losses theat Willis speaks about moderate the climate (thunderstorms, clouds, winds, etc.).

It is important to distinguish cloud formation from cloudless humidity. The latter is a positive feedback. The former is a negative feedback.

More clouds at the same humidity means cooling.

More humidity at the same prevalence of cloud formation means warming.

AFAIK, around ambient temperatures, the derivative of partial pressure versus temperature (dP/dT) is small. Consequently significant positive feedback from water vapor is quite dubious. Conversely, the reflectivity of clouds is large, meaning variations in cloud formation are significant.

So things are quite misleading when you tie cloud formation primarily to vapor-pressure. It makes clouds appear to be positive feedbacks. But there is some evidence that cloud formation variation is closely tied to cosmic-ray flux.

Steve S: I should also mention that my sensitivity estimates account for all feedbacks, both positive and negative, since the estimates are made from actual observations (30-year averages) in temperature and radiation at the surface. They include the factors you mention, and that is why they vary from 0.03 to 0.22 deg/wm-2, depending on location.

The GCMs assume that relative humidity remains constant as the atmosphere warms, an assumption which leads to a water vapor increase of about 7% per K near the surface and about 15% per K at the cold, high altitudes. The most important region for trapping radiation is at high altitudes (300mb) and in the outer tropics (10-30 degrees latitude).

Since we’ve seen maybe 0.3K increase in global temperatures in the satellite era it seems like some increase in upper-troposphere water vapor might be noticeable by now. The evidence is mixed, which is not surprising given the small predicted change in something that shows large interannual variability.

Weather balloons, which are for meteorological (not climate) purposes and have limitations, generally haven’t shown an increase in mid- and upper-level water vapor. I have been looking for humidity results from the high-quality RATPAC balloon network but have found nothing so far.

The reanalysis data, which combines observations plus computer-generated values to fill in any blanks, shows a general decline in mid- and upper-level water vapor in recent decades. Some people quickly dismiss reanalysis data, but it is based on physical principles and is a nagging inconsistency with the GCM prediction.

There is some evidence from satellite data (see FAR) that upper-level water vapor content has increased in the last 25 years as the upper atmosphere warmed but there is large interannual variability, including a sensitivity of water vapor to ENSO changes. How much of any higher upper-level humidity is due to CO2-induced warming and how much is due to greater El Nino activity?

The location of any water vapor increase is also important (higher water vapor in rainy tropical regions has less impact on global warming than does higher humidity in the dry regions where the air radiates away its heat and descends). The data duration is just too short to say much about location, from what I’ve seen.

Other satellite data can be found in a study discussed on Earth Observatory. It showed that, at high levels of the atmosphere, water vapor has increased but not nearly as much as assumed by the models. (Oddly, I can’t find that article tonight on Earth Observatory. I’ll keep looking. I hope it has not been pulled.)

So, in my opinion the jury is out as to whether water vapor (and water vapor feedback) are behaving as predicted by the GCMs.

The GCMs assume that relative humidity remains constant as the atmosphere warms, an assumption which leads to a water vapor increase of about 7% per K near the surface and about 15% per K at the cold, high altitudes. The most important region for trapping radiation is at high altitudes (300mb) and in the outer tropics (10-30 degrees latitude).

How does that work out exactly? Water evaporation requires 2.2kJ/gram. The basic physics of greenhouse warming is that temperatures rises until radiative flux out matches radiative flux in. i.e., there isn’t more radiative energy on the first order. Granted, once the temperature of the air rises, there is more flux into the oceans. Thus, more evaporation, but this evaporation cools the air temperature. Obviously this doesn’t balance out, so I assume there is little change in the evaporation of the oceans as the air temperature rises.

Do the models assume an instantaneous doubling of CO2 or a constant increment of 2.8 ppmv a year for 100 years? I looked at Held & Soden and couldn’t figure it out. This is a nonlinear system so the response will be very different depending on how the CO2 is injected into the atmosphere.

Re#17 Hi, JMS. The water content of the tropical upper troposphere is determined by how cold air parcels become (= how high they ascend in tropical thunderstorms) and some other, probably less-critical factors like the extent of sratiform precipitation (which evaporates and moistens the air over a large area as it falls). I’m pretty sure that Held and Soden support this conceptual view, as they have written about the topic (and written well – they are excellent writers) and may have originated the air parcel visualization.

Air parcel and precipitation behavior on rather small scales are complex and are things with which climate models struggle. I don’t think there are simple first principles that would help. My understanding is that the models make simplifying assumptions about tropical cloud behavior, which may be right or may be wrong – we just don’t know.

from looking at the Held/Soden ppt it seems as though the increase in water vapor is derived from first principles.

Well, I haven’t finished reading the entire paper yet, but from what I’ve seen up to page 10, there are a bunch of very important assumptions made to derive the results they present. Things like constant RH, no cloud changes, etc. To claim that this is from “first principles” isn’t correct, IMO.

Of course maybe when they get to objections they’ll show persuasively that these are correct assumptions, but I’m afraid they’ll pull a fast one and essentially end up begging the question.

Re 316 Paul A, I may be missing your question with this but I’ll give it a shot regardless. Let me know if I’m off the mark.

The moisture content of the lowest levels of the tropical maritime atmosphere is determined, to a large extent, by the vapor pressure of the sea surface, which is determined by temperature. Water evaporates and mixes into the bottom several thousand meters of the atmosphere. As the relative humidity rises, the evaporation rate slows and reaches an equilibrium. I think this part of the water vapor cycle is non-controversial.

The moisture content of the upper atmosphere is determined by the extent to which air parcels ascend (and some other things). I think the models assume that, in an AGW world, the air parcels (clouds) rise but don’t become as cool as they do in a non-AGW world. Since they haven’t cooled as much, their water content is higher. The cloud then evaporates as it travels through the upper atmosphere, adding this extra moisture to the upper levels.

The 7% and 15% are based on the water content of constant-relative-humidity air at their respective temperaures, as their temperature changes by 1 K.

The evaporation rate from the tropical ocean may change little in a warmer world, once enough moisture has evaporated to raise the water content of the lower (mixed) layer of the atmosphere to a near-equilibrium level.

Positive feedback as in water vapor or CO2 in ice age glacial – interglacial cycles is generally considered to be an amplifying factor. For instance doubling of CO2 is though to increase greenhouse effect with some 1-1.2 degrees, it’s the water vapor feedback that is thought to amplify it to 1.5 – 4.5 or something. But that’s not the mechanism of feedback. Amplification is merely steering a system with an input independent of the output. Feedback closes a loop and a system is steered partly by it’s own output added to the original (natural) input.

Negative feedback steers against the system output, so if natural variation causes a excursion, negative feedback steers it back and stabilizes the system. Daisy world of James Lovelock is a natural negative feedback system. The speed / cruise control of your car is too.

Positive feedback is the opposite, adding a feedback to the system in the same direction of the excursion, hence it is steering the system away from a certain output until it’s limits are reached, Hence the system is only stable at its limits and unstable in between. This also signifies that there is a very clear difference between system input (natural variation) and system reaction. At the limits a small natural variation can trigger the flip to the other stable position. Halfway the system is very insensitive from variable input as the strong positve feedback takes over the input. Therefore it is very easy to test if there is positive feedback in a system.

Olavi Karner finds no signs of positive feedback in the atmospherehere

and I don’t find any sign of positive feedback here of CO2 in the warming after the last glacial period in the Dome C ice core of the EPICA project:

jae, just speculating, but the “overall” water vapor vs temp effect, including clouds, could be somewhat like the inverted quadratic tree growth/temp effect — rising steeply upward from initially low concentrations, leveling out & then downturning & even going negative w/high concentrations, such as the tropics or other humid areas.

The Karner paper was published in 2002. There have been significant corrections in the MSU temperature data since then. When someone runs the same analysis using the current data and gets the same results, I’ll be more impressed.

As far as the chart, again, all it proves is that CO2 is not the primary driver of temperature change from glacial to interglacial and that CO2 concentration is somewhat dependent on temperature. This is not news. We already know that CO2 varies with temperature from the seasonal variations measured at Mauna Loa. The other thing it proves is that the primary forcing that ended the glaciation is not constant, or even monotonic. The Huelmo/Mascardi Cold Reversal, reflected by the drop in temperature from about 14,000 to about 12,500 y BP in the chart, is a clear example of that. In the Northern Hemisphere the similar phenomenon at about the same time was called Younger Dryas. Without knowing the actual solar forcing as a function of time plus the change in albedo with time and several other things like ocean currents and ice extent, it is not possible to prove or disprove a contribution from carbon dioxide to the overall temperature change based on the ice core data alone.

Thanks for your post, plot, and links. You presented an excellent plain-English description of the fundamental feedback issues (and I suspect English is not your first language!) for the non-specialists. As someone whose degrees are in (engineering) feedback control systems, I’d like to add a couple of quick points. You say:

Positive feedback is the opposite, adding a feedback to the system in the same direction of the excursion, hence it is steering the system away from a certain output until it’s limits are reached, Hence the system is only stable at its limits and unstable in between.

To those who argue that CO2 plays an important positive-feedback role in the glacial-to-interglacial transition, the direct implication of that argument is that the capability of that positive feedback must have stopped at about present conditions, because the system limits were reached. And it did so at approximately the same point in multiple transitions.

When people of my background (and many have commented at this site) look at plots like the Vostok temperature/CO2 plots, the conclusion we reach is that the present climate, like most periods outside the glacial/interglacial transitions, is dominated by stabilizing negative feedback effects. While those plots are used to scare a lot of people, I am actually reassured by them.

Another point: a time lag in feedback, whether negative or positive feedback, is destabilizing. If the ~800-year-delayed CO2 response were indeed a positive feedback, it would have had much more of a tendency to shoot the climate to a state far hotter than what recent interglacial periods like the Holocene have been. (I’m in the middle of a new electronic design right now where I’ve added a 10-microsecond delay in the [negative] feedback processing to obtain better noise rejection, and I’m fretting about the destabilizing effects this will have.

The Karner paper was published in 2002. There have been significant corrections in the MSU temperature data since then. When someone runs the same analysis using the current data and gets the same results, I’ll be more impressed.

As far as I know, there has only been one significant correction to the MSU temperature data since 2002, which changed the trend somewhat in the tropics. However, this would have only the most minimal effect on Karner’s work, as it concerned the Hurst statistic.

The Hurst statistic measures long-term correlation (persistence). It is not concerned with the trend, but with historical relationships. I have not redone Karner’s work, but I see no reason to expect that the slight change in trend would have more than a very minimal effect on the Hurst statistic, and no effect on the paper’s conclusions.

Slide 29 from Held and Soden has a remarkable shift in the climate sensitivies due to some model changes.

The NAS book speaks about the uncertainties around clouds and their impact:

“If the structure or area coverage of clouds change with the climate,
they have the potential to provide a very large feedback and either greatly
increase or decrease the response of the climate to human-caused forcing.
At this time both the magnitude and sign of cloud feedback effects on
the global mean response to human forcing are uncertain.”

Then they compare higher-sensitivity GFDL model (4C for doubled CO2) and NCAR model (2C for doubled
CO2); difference is “in the response of low marine boundary layer clouds
in the two models”, they decrease in GFDL model and increase in NCAR model.

So 2 models, both are valid and one has a 2X impact on climate than the y other?
Hmmm. Then in slide 30, the ‘new’ model now shows agreement, mostly to the lower value.

If there has been an adjustment to some standar models that cut the CO2 sensitivies in half,
isn’t this a big deal? 750ppm CO2 leads to 2C versus 4C increase?

Thanks. 30 years ago during my *Dutch* education I passed along system response but I remember the basics. Now, I’m looking at a lot of correlating proxy graphs of the Pleistocene ice age, especially the oceanic proxies, which system response interaction does not make sense, considering the explanation. Inertia doesn’t seem to exist, for instance, or are we looking at completely different things? There is no such thing in geology or paleoclimatology of judging system parameters in terms of in- and output and system delay.

I believe that here we can find the needle to punch right trough the hot air balloon of global warming. But I could certainly use the help of a system engineer for the details.

The Earth Observatory article on upper-troposphere water vapor measurement is here . It uses satellite data and reports that upper-troposphere water vapor has increased in recent times but not as much as the models assume.

There is no mention of this study in IPCC FAR.

Open questions include whether any increase in recent decades is driven by CO2-induced warming or is due to increased El Nino activity. Also, the location of any water vapor increase is important.

If I recall correctly, this study measured things a little higher in the atmosphere (100-200mb?) than would be ideal (300-500mb).

Also on Earth Observatory is an older article on Lindzen’s iris hypothesis. He does now have some radar-derived evidence in support of his thoughts, but one has to make some significant assumptions to extrapolate those results to an AGW world.

I’ve skimmed through the Held & Soden 2000 paper now. It’s clear that the big problem is that it concerns itself solely with the clear sky water vapor feedback. The clearest statement is on p15

Because cloud and water vapor feedbacks are obviously related at some level,
they are often confused in popular discussions of global warming. In the current generation of climate models, water vapor feedback is robust and cloud feedback is not. A robust water vapor feedback sensitizes the system, making the implications of the uncertainty in cloud feedbacks of greater consequence.
The total radiative effect of increases in water vapor can be quite dramatic, depending on the strengths of the other feedbacks in the system. For the remainder of this review we return our focus to water vapor feedback in isolation, represented by beta(H2O) in the preceding discussion.

IOW, they agree that the crucial point is how water vapor affects clouds, but since that’s not well known they’re going to ignore it. And, in essence, they blame those of us skeptical of the total sign of water feedback for not being willing to ignore clouds too.

The point is that I don’t have any big problem with calculations of open sky feedback of water vapor on radiation. I’d certainly expect it to be positive and perhaps strongly so. Where I do have a problem is with how to evaluate the total of all affects of water with rising temperature. We have not just the direct radiative affect, but also the change in cloud cover / albedo and the increase in convective transfer of heat from the surface to higher levels of the troposphere (i.e. evaporation / condensation. I’m not worried about the terminology (feedback vs forcing) or the name we go under (Cloud vs Water Vapor)I just want all the affects to be considered before claiming that the temperature changing affects of CO2 is amplified by water.

An artifact of the diurnal correction applied to LT
has been discovered by Carl Mears and Frank Wentz
(Remote Sensing Systems). This artifact contributed an
error term in certain types of diurnal cycles, most
noteably in the tropics. We have applied a new diurnal
correction based on 3 AMSU instruments and call the dataset
v5.2. This artifact does not appear in MT or LS. The new
global trend from Dec 1978 to July 2005 is +0.123 C/decade,
or +0.035 C/decade warmer than v5.1. This particular
error is within the published margin of error for LT of
+/- 0.05 C/decade (Christy et al. 2003). We thank Carl and
Frank for digging into our procedure and discovering this
error. All radiosonde comparisons have been rerun and the
agreement is still exceptionally good. There was virtually
no impact of this error outside of the tropics.

I think this qualifies as a significant change even if it was less than their quoted margin of error. However, if you say this doesn’t affect the Karner’s calculation, I will concede the point.

I’m still not sure about the overall point of this thread, though, when there are so many other points where climate models are admitted to have large uncertainties like clouds and the wide range in the estimates of most forcings. Then there is the exclusion of other forcings like whatever produces the 1500 year climate cycle and the inclusion of aerosols that seems to have no observable basis other than the need for a fudge factor. Maybe this is meant to be an indirect attack on the apparent assumption of all modelers that there are no negative feedbacks. If so, it’s so indirect that I think most readers may completely miss the point.

I still think it’s possible that the models are correct, as far as they go, but that the combination of a warm bias in the instrumental record and an underlying trend from forcing(s) not included in the models makes their predictions come out wrong.

Actually, changes in clear-(upper)air water vapor are quite important, because of the large area that clear air occupies and because that’s a window where IR escapes.

A current global view of the Pacific Basin is here . In this colorized IR image, high clouds in the tropics are bright white while clear (upper) air is blue or light gray. The ITCZ is visible as a discontinuous string of clouds near the Equator while the Indo-Pacific Warm Pool convection (big thunderstorms) is on the left. That’s a lot of blue in the regions (East Pacific) where upper air radiates away a lot of heat and sinks.

If that blue-region radiation becomes hampered then heat accumulates and, I suppose, the function of the Hadley-Walker heat removal conveyor is affected.

It’s not at all clear that water vapor has increased in the blue regions, at least not to the extent assumed by the GCMs.

For fun, here’s the water vapor image for the Pacific, which shows water vapor in the middle and upper atmosphere. It is hard to make sense of the colors at first, but red are rain and thick clouds, yellow is cirrus and high humidity and green and blue are clear-air regions where the air cools and sinks. Note the swirling lumpiness of the tropical atmosphere – upper level water vapor comes in clumps, which is generally not recognized.

re 20:
I don’t know, as far as I know it takes years before volcanic aerosols are removed from the tropopause, and I do know that the tropopause is bone dry, so IMHO air traffic water vapour has a long residence time at the tropopause. Perhaps this publication can tell:

RE: #38 – Allow me to profer some wild (but informed) speculation. Most if not all GCMs fail to account for the vast areas of the Earth’s surface between 20 and 40 deg N latitude which experience compressive, subsiding regimes, due to the massive semi permanent semi tropical anticyclones. Taken as a global whole, with similar topographically driven compressively dominated zones (for example, the high plains just to the East of the Rockies), such places account for the lion’s share of the blue areas at any given time.

A presentation by Soden is here . This discusses the satellite-derived evidence for moistening of the upper troposphere, which is very important to the GCMs.

They make the best use of the data that’s available, but that data has shortcomings. To reach their conclusions (slides 8 and 9), one has to:

* prefer the RSS satellite temperature data over the UAH data

* assume that the water vapor channel (T12) is measuring the same part of the atmosphere as the temperature channel (T2).

Figure 2 of this RSS website shows the atmospheric weighting of channel 2 (“TMT”). Most of the weighting is in the lower troposphere, below about 6km.

Figure 1.10 at this website gives an idea of the weighting function of channel 12, which is concentrated at above 6km and has little representation below 4 or 5 km.

That would make little difference if the temperature throughout the troposphere has been changing uniformly at all altitudes, but even the RSS data (see above website) for lower-troposphere and middle-troposphere levels leave me wondering if that is a valid assumption. The satellite data seems to indicate that lower levels have warmed more than upper levels.

I believe that channel 12 (see slide 8) measures relative humidity and shows (black line) that relative humidity of the upper troposphere has changed little in the last 20 or so years. But, they assume that the upper troposphere has warmed, and therefore to maintain constant relative humidity there has to be more moisture in the upper troposphere.

Their critical assumption is that the upper troposphere has warmed, and warmed as much as RSS channel 2 (TMT, which has a significant weighting in the lowest troposphere) says it has warmed. Maybe, maybe not. And even with that assumption, slide 9 says that “the authors conceded there are some magnitude issues”.

I think this study is a key part of the FAR technical report.

Again, the authors are making the best effort they can with limited data, but to me the jury remains out as to the extent of upper atmospheric moistening, and location of the moistening, and how much is due to ENSO factors.

I read the Climate Science discussion on humidity, referenced in #44. Thanks again, Paolo, for pointing this out, as I had missed it.

In this discussion, a study reports no detectable change in global precipitation in the last 25 years and Pielke Sr sees that as evidence that humidity (water vapor) has not increased, contrary to the claim of the IPCC.

I agree with Held that water vapor, temperature, evaporation and precipitation are not tied together in the straightforward way that Pielke Sr suggests. Also, the change in temperature has been so small that the predicted change in precipitation is probably undetectable. So, the study that is mentioned offers little evidence, one way or the other, that water vapor has changed.

Having said that, though, I do think the IPCC statement overstates its case. It subtly convolutes two types of humidity change. The “important” humidity change is that which occurs at high altitudes, especially in the tropics. The “unimportant” humidity change is that which occurs near the surface, which adds little to the greenhouse effect and really should be left out of the discussion except as a footnote.

The evidence for “unimportant” near-surface water vapor increases is solid; the evidence for “important” high-altitude increases is anything but solid. The IPCC uses the phrase “broadly consistent” which is one of those phrases that means little, especially on a subject where small changes make a big difference.

47: Steve S: I don’t understand much about that article and don’t have time to study it. However, one thing I noticed is that they divided temperature by watts/m2 to derive a climate sensitivity numbers. As I recall, Gavin at RealClimate told me that you can’t do that (something like, “you can’t just divide any old temperature by wattage to get sensitivity.”

The key thing they try to do is to discredit the notion of “dry windows” in lower latitudes allowing lots of outward radiation of heat into space. They don’t even really address lower midlatitude areas of persistent subsidence which have very hot day time summer temps (with corresponding massive outward heat flux at night). Would love to have David Smith debate the two authors – popcorn time …. LOL :)

The key thing they try to do is to discredit the notion of “dry windows” in lower latitudes

I’d say the key thing is that they don’t consider clouds in their models. Sure the positive feedback sensitivity of CO2 is of some importance but more important is just how clouds work (if they do) as a negative feedback. And they say that the models are all over the place even though they’re all set up differently. This sounds to me like tuning to meet expectations.

Anyway that’s a pretty old paper. Has it been updated or did they publish a paper on the cloud feedbacks?

Pielke Sr has an interesting article ( link ) on regional changes, or the lack thereof, in atmospheric water vapor in recent decades. Now the study is geograpically limited and does not address the issue of high-altitude vs low-altitude changes in water vapor (high-altitude water vapor, a small part of the total, is nevertheless quite important) but it does present results that are broadly inconsistent with (my understanding of ) the GCM outputs.

The Wang et al study covers North America, Greenland and adjacent ocean. It uses reanalysis data which I believe is based on satellite-derived values for ocean areas and radiosonde values for land areas, though I may be wrong in that assumption.

The Wang study found no trend in lower-atmospheric water content over North America despite evidence of lower-atmospheric warming. The significance of North America is that it is a well-measured region.

The GCM-based expectation is that water content should have risen during the atmospheric warm-up. Why didn’t sensor-rich North America behave in that manner?

BTW, my # 51 should have said, “GCM inputs”, not outputs. My understanding is that constant relative humidity is an assumption which is plugged into the models and is not an output.

Re #53 – I had a comment from someone that Soden is just a regional study over a limited time period. That is why I was asking where the data was. When I looked at the paper, there was no data or archive source attached.

Re #55
Pat Keating says:
December 18th, 2007 at 9:24 pm
39
“Hans, someone has pointed out on this blog that there is a little water vapor at the tropopause from methane (which is less dense than air), oxidized by ozone.”

Rather than density unlike water it doesn’t condense but once it gets into the stratosphere it can react to create 2 molecules of water.

Just an observation on Held-Soden slides show. They insist on attribute the increase of water vapor to doubling CO2 instead attributing it to the increase of temperature. Temperature can increase or decrease without doubling or decreasing the atmospheric CO2 concentration. Held-Soden conference is biased.

There are climate changes not attributable to any known forcing, external or internal, but to the existence of a free stochastic internal variability. Climate is always unstable; we can never talk about climatic equilibrium.

Jae proposes a negative feedback of water vapor and I think we have misunderstood him. I believe that Jae is right at least in a 49.99%. Why he is right at least in a 49.99%? Because water vapor forming clouds reflects 29.99% of the Solar Radiation incoming to Earth, and diffuse water vapor in the tropospheric lower, middle and upper layers absorbs 20% of the incoming solar radiation; thus, only 50.01% of the incident solar radiation upon Earth is absorbed by her surface. It is a cooling effect… unquestionably. Those 20% of solar radiation absorbed by diffuse water vapor is transformed into potential and kinetic energy that is dispersed by radiation toward the cold outer space when water vapor condenses. The same occurs with the latent heat of phase change of water; 24% of the energy absorbed by the sea surface is transferred to the water phase change in form of latent heat of evaporation, which is released by radiation to the cold relative void when water vapor condenses and solidifies at the upper layers of the atmosphere. Thus, adding 12% of the latent heat to 49.99%, we obtain a cooling effect of ~62% from water vapor.

Yes, yes, yes, I know… Water vapor absorbs more energy than carbon dioxide… Thus the state of things, water vapor steals energy from his companion the carbon dioxide and from the dry atmosphere and take that energy up to the tropopause and release it to the cold deep void. ;)

Hans, someone has pointed out on this blog that there is a little water vapor at the tropopause from methane (which is less dense than air), oxidized by ozone.

I add- ozone, which is much more dense than air, so how the heck do they coexist for long at the same level?

Ever since the ozone hole theory started, I was dimayed by the ready acceptance of a set of chemical equations derived in the lab being applied to the atmosphere at great altitude. I still disbelieve that the chemistry is quantitative and has predictive power. I believe that ozone has shot into prominence and has been ascribed peculiar behaviour that time will prove fanciful, but popular because it is hard to gather evidence to argue against it. I cannot offer a quantitative alternative model, I lack the boundary conditions/assumptions. Yet this heavy ozone is now implicated in the definition of the tropopause and is held to be a reason why the temperature gradient inverts there. Some chemical, this ozone. The Rosetta stone of global warming, almost.

My main question/concern about the Soden Held analysis is that it doesn’t address the question of mositure changes in the clear-air regions of the tropical upper troposphere. Those are the regions where the air lifted by tropical thunderstorms radiates, cools and sinks. It’s not that the study is wrong but rather that it is limited in scope and thus silent on this key issue.

The IPCC uses the study in its defense of the constant relative humidity assumption but I think this study is not as strong a defense as they portray.

I add- ozone, which is much more dense than air, so how the heck do they coexist for long at the same level?

The same reason that CO2 doesn’t collect at ground level, diffusion and convection, separation of gases by mass doesn’t happen until ~100km

I cannot offer a quantitative alternative model, I lack the boundary conditions/assumptions. Yet this heavy ozone is now implicated in the definition of the tropopause and is held to be a reason why the temperature gradient inverts there. Some chemical, this ozone.

You apparently also lack the necessary knowledge of Physical Chemistry, I suggest you start to remedy this by reading up on the kinetic theory of gases.

#2 John Hekman A more accurate statement is that data from some satellites shows no warming trend at certain layers of the atmosphere as an average for the layer, and a warming trend at other layers of the atmosphere (and sea surface) as an average of the layer.

—————-

#8 Jason L Exactly; Who cares what “would happen”? “if there were no feedback” is meaningless, because reality has feedbacks.

——————

Mesosphere: Metalic atoms, noctilucent clouds, -100 C or so.
Stratosphre: Warmer up(-3C), cooler down. Ozone absorbs UV and heats. Water vapor some. Lower at poles, higher equator.
Tropopause: Dry air at -50C Lapse rate 6.5C/km from troposphere to here, once the lapse
rate gets under 2C/km and then starts increasing, stratosphere. No hard boundry (e.g. tropical thunderstorms overshooting into the lower stratosphere (positive lapse rate).
Troposphere: Gets warmer on the way down (negative rate going up, until it hits an average of 15C at the surface, 80% of the atmosphere’s mass. Lots of vertical mixing. Mostly water vapor and aerosols make up the mass.

How much IR gets through for the CO2 in the first place? (Assuming there aren’t clouds in the way in the way.)

—————-

The chemical composition of the troposphere is essentially uniform, with the notable exception of water vapor. The source of water vapor is at the surface through the processes of evaporation and transpiration. Furthermore the temperature of the troposphere decreases with height, and saturation vapor pressure decreases strongly with temperature, so the amount of water vapor that can exist in the atmosphere decreases strongly with height. Thus the proportion of water vapor is normally greatest near the surface and decreases with height.

If the air contains water vapor, then cooling of the air can cause the water to condense, and the behavior is no longer that of an ideal gas. If the air is at the saturated vapor pressure, then the rate at which temperature drops with height is called the saturated adiabatic lapse rate. More generally, the actual rate at which the temperature drops with altitude is called the environmental lapse rate. In the troposphere, the average environmental lapse rate is a drop of about 6.5 °C for every 1 km (1000 meters) increase in height.

Depending on the weather conditions, one may find that the environmental lapse rate (the actual rate at which temperature drops with height) is not equal to the adiabatic lapse rate. If the upper air is warmer than predicted by the adiabatic lapse rate, then when a parcel of air rises and expands, it will arrive at the new height at a lower temperature than its surroundings. In this case, the air parcel is denser than its surroundings, so it sinks back to its original height, and the air is stable against being stirred. Such a situation is called temperature inversion, and can lead to the trapping of air pollution in basins such as that of Los Angeles. If, on the contrary, the upper air is cooler than predicted by the adiabatic lapse rate, then when the air parcel rises to its new height it will have a higher temperature and a lower density than its surroundings, and will float. Such a process can happen spontaneously, and under such conditions, the air will be stirred by spontaneous convection currents

What is the volume of air in a 5×5 degree grid (say 0-5 lat 0-5 long) that goes up ~80 km (guessing the below stops around the mesopause boundry and doesn’t count all the way the full 10,000)

The mass would be 3.85 billion metric tons (5000 trillion/1296) I believe. Volume?

The average mass of the atmosphere is about 5,000 trillion metric tons or 1/1,200,000 the mass of Earth. According to the National Center for Atmospheric Research, “The total mean mass of the atmosphere is 5.1480×1018 kg with an annual range due to water vapor of 1.2 or 1.5×1015 kg depending on whether surface pressure or water vapor data are used; somewhat smaller than the previous estimate. The mean mass of water vapor is estimated as 1.27×1016 kg and the dry air mass as 5.1352 ±0.0003×1018 kg.”

Let’s summarize this feedback mechanism now. Extra CO2 leads to extra IR at the surface, which evaporates more water, which ROBS the surface of the energy for vaporization, which is a NEGATIVE feedback at the surface and LOWERS surface temperature. But the water vapor then rises to some altitude where it radiates more IR to the surface, which causes more water vapor to evaporate, which ROBS the surface of even more energy for evaporation and lowers the surface temperature even more. And this all leads to an increase in temperature at the surface? Im confused.

Meanwhile, back at the ranch near Phoenix, there is very little water available, so there can be no water vapor feedback. But the average July maximum temperature is a whopping 40.6 C, and the average is 33.6 C. The average minimum is 26.7 C. Yet, with all the water vapor in my other ranch in Pointe-Noire, Congo, at 4 degrees S. latitude and 17 m elevation, the maximum average temperature (29 C) never goes much higher than the minimum in Phoenix. I am definitely confused.

Version 1) CO2 captures IR from the surface and re-emits it as IR photons, 50% up and 50% down, thus the downwelling IR raises surface temperatures. The upwelling IR raises temperatures higher in the atmosphere until eventually it is radiated to space.

Version 2) CO2 captures IR from the surface and thermalizes it. Re-emission is insignificant. Once the IR is absorbed, it is heat. This would heat the surface air only. Any re-emission would be spontaneous, at other wavelengths. The CO2 wavelengths would look dark from space. With this scenario, there is no such thing as downwelling radiation.

I invite comments on this. Which is the effective process at the earth’s surface?

jae, it would seem that when the AGHA absorb IR and interact with each other to create energy, the heating evaporates water into vapor which absorbs energy in the process, creates more IR absorbing substances, and provides another gas to interact with the others. At the start, it’s aborbing more energy than it’s providing, until it starts providing more energy than it’s absorbing. At some point there’s not enough incoming energy to cause any more heating from the process, but it’s higher than it would be without the water because of its contribution.

I’d guess in areas with little water, the weather patterns sadlov talked about, coupled with the surface properties, lack of clouds to block much of the sun, and the sun’s angle create more energy in the first place, just that the energy doesn’t have to heat any water.

Scenario 1, desert: X amount of sun, land type and the weather patterns heats an area to 150

Scenario 2, coast: Y amount of sun, land type and the weather patterns that would normally heat an area to 75 heats it to 100 because of the water’s contribution.

68 pochas
At the earth’s surface, version 2 has to be the correct one. Version 1 may be the correct one at higher altitudes, where molecules are fewer and farer between, and also colder (so moving more slowly). I don’t know at what altitude the probability for re-emission becomes equal to the probability of thermalization — perhaps somebody else can help there.

RE: #72 – Reality check. Phoenix in early January. Daytime highs would typically range from the mid 50s to the low 70s (depending on weather pattern). Lows from the 20s to 40s. July – highs range from upper 90s to upper 110s, lows from 70s to 90s. You’ll never get a 150 – 30 swing at / near the substrate.

72, 73, 74: See my post on Unthreaded. The LOWs in Phoenix in July are alomost as high as the HIGHS at the Equator. If water (GHGs) were producing any noticable increase in temperature, I don’t see how this can happen.

OOooops. I answered that in unthreaded. Well in 1913 it got up to 134 in death valley as we know, but I can’t find the low for the day. :(

Jouf Saudi Arabia, July 3 2002 74 low 107 high (random city, random year, hottest month, I think I took the hottest day in the month)
Phoenix July averages 81 to 104
Las Vegas July 13th 1972 48 low 119 high

I was generally talking about the kind of desert where they probably don’t have thermometers or records; dry, low, no vegetation, no water, no clouds, sand dunes. Lots of sun, quick release of heat by the ground, no water to store heat in the ground. No water to hold energy in the day to release at night, bigger swings, higher temperatures quickly cooling a few 10s of degree F. Seems easy enough. YYMV.

75: There are thousands of places all over the Globe that show the same thing. For example, check out all low-elevations in Iraq, and compare the LOWs to the HIGHS in low MOIST areas near the Equator. Here’s one source of data for such an exercise.

75: Also, the average absolute humidity in Phoenix in July is 12 g/m^3. Moist areas at similar elevations and latitudes have absolute humidities about twice that, yet they are cooler, as measured by Tmax, Tmin or Tavg. Water exerts a negative influence on temperature, simply due to the impact of the heat of vaporization. And I don’t see evidence that that heat is returned to the surface by water or CO2 or any other AGW-type mechanism.

Over the period of June 1991 to December 1995, the standard model predicts an average global cooling of 0.31 K, which compares favorably with the observed cooling of 0.30 K [0.33 ± 0.03K, with ENSO signal removed].
Without water vapor feedback, the model- predicted cooling is only 0.19 K. Thus, feedback from water vapor amplifies the magnitude of global cooling by approx. 60%, which is in good agreement with the amplification predicted by climate models in response to a doubling of CO2 and with that derived from idealized calculations using a constant relative humidity approximation.

I read this as saying the climate sensitivity, with water-vapor feedback, is around 1.7 – 2.0ºC per 2xCO2, or at the low end of the IPCC guesstimates. Do you agree?

We calculate an observed water vapour feedback parameter of 1.6 Wm2 K1, with uncertainty placing the feedback parameter between 0.9 to 2.5 Wm2 K1. The uncertain is principally from natural climate variations that contaminate the volcanic cooling…

I don’t have the figures at hand, but I bet SM or someone else does: do Forster & Collins agree (±) with Soden et al? What does this translate to as a climate-sensitivity number? Are we on the track of a real, empirically-derived CS number?

We determine the volcano climate sensitivity λ and response time τ for the Mount Pinatubo eruption, using observational measurements of the temperature anomalies of the lower troposphere, measurements of the long wave outgoing radiation, and the aerosol optical density. Using standard linear response theory we find λ = 0.15 ± 0.06 K/(W/m2), which implies a negative feedback of −1.4 (+0.7, −1.6). The intrinsic response time is τ = 6.8 ± 1.5 months. Both results are contrary to a paradigm that involves long response times and positive feedback.

I’m not sure what the dimensionless -1.4 means. Help?

Their numbers were disputed by Wigley, Ammann et al, and I don’t know how that came out. The comment’s not free online, at AGU anyway.

In summary, we have shown that Hansens hope that the dramatic Pinatubo climate event would provide an acid test of climate models has been achieved, although with an unexpected result. The effect of the volcano is to reveal a short atmospheric response time, of the order of several months, leaving no climate in the pipeline, and a negative feedback to its forcing.

In conclusion, neither the physics nor the results in the DK paper are correct. Their unconventional result that the climate sensitivity is very low is simply an artifact of their use of an over-simplified model to fit the observed cooling from Pinatubo.

OK, they’re in a huff that DK got such a low sensitivity figure (which nobody quotes, dammit). Surely this has been discussed here? We know how scrupulous Ammann is with his numbers…

–it’s a 2004 conference paper, said to be a continuation of
D. H. Douglass and B. D. Clader, Climate Sensitivity of the Earth to Solar Irradiance. Geophys. Res. Lett. 29, doi:10.1029/2002GL015345 (2002). (which I haven’t seen)

Summary:

We find the climate sensitivity to the 11-year variation in solar irradiance to be about twice that expected from a no-feedback Stefan-Boltzmann radiation balance model. This gain of a factor of two implies positive feedback…
Response times of the order of 3 months are found for both solar and volcano forcing…

Hmm. I don’t really understand this one, either. Interesting graphs at the end of the pdf. More homework required. Translation to standard English appreciated ;-)

Since increasing water vapor increases convection which increases both clouds (aka albedo) and latent heat movement from the surface, and that’s the biggest challenge, how do we even know the sign of the water vapor feedback, let alone the magnitude?

The largest cooling in the summer of 1992 was in the center
of North America (Plate 3). As a result, the ice on Hudson
Bay melted almost a month later than normal that year. Polar
bears, who feed and have babies on the ice, were much heavier
and had more healthy cubs that summer. Biologists call
those now 11-year olds Pinatubo Bears [Stirling, 1997].
The cool conditions in the summer after the Pinatubo eruption
was very beneficial for the Hudson Bay polar bears, and
there were many more bears born that year than the year
before or after. The long-term concern for these bears, and
many other plants and animals in the Arctic, however, is the
opposite impact from global warming. This temporary positive
impact from Pinatubo strengthens the argument of the
negative impacts of the predicted warming. Pinatubo produced
global cooling, but impacts work in both directions, so
the benefits of Pinatubo from global cooling teach us about
the negative impacts of anthropogenic global warming.

“This temporary positive impact from Pinatubo strengthens the argument of the negative impacts of the predicted warming…” Gee, that makes sense…

Peter – at 60% amplification (your #80) to the 1.5 K bare CO2 effect, that would be 2.4 K warming for a doubling of CO2. However, that is the short-term temperature response; long-term response (as we’ve been sort of discussing on the glacier thread) could be twice as large from the slow warm-up of oceans, ice, and other parts of the system. Sensitivity is an equilibrium number – long-term average, not short-term. So a delta-function experiment like Pinatubo gives a lower bound, but not much more than that.

…at 60% amplification (your #80) to the 1.5 K bare CO2 effect, that would be 2.4 K warming for a doubling of CO2.

Or 1.6 to 2.2, using the “usual” range of 1 to 1.35 I’ve seen for this. Do you hae a cite for the 1.5? Odd that this is still being debated, 100+ years after Arrhenius…

Thanks for the tip on the glacier thread, which I haven’t been following. As you know, response times are under vigorous debate. In any case, it’s good to have an empirically-derived number, even if that seems squishy — see P. M. de F. Forster and M. Collins in #84, which I haven’t had time to sort out (and hoped someone else would first ;-) )

Everyone needs to remember that the average amount of water vapor residing in the atmosphere is not a function of the evaporation rate. It is a complex combination of processes that are connected to both the evaporation rate AND the precipitation rate.

Renno, Emanuel, and Stone years ago showed that by simply increasing the precipitation efficiency of precipitation systems, a cooler climate with LESS precipitation results. So, why do we never talk about the controls on precipitation efficiency?

Well, we spend so much time discussing how EVAPORATION changes with temperature, wind, etc, because we can MEASURE these things at the surface — where we live — any time we want. We see evaporation happening right before our eyes. We feel it on our skin. IN CONTRAST….the processes controlling precipitation efficiency are hidden from us, within the clouds where microphysical processes are doing their thing.

Ultimately, water vapor and cloud feedbacks are likely tightly connected to each other and to precipitation processes.

Everyone needs to remember that the average amount of water vapor residing in the atmosphere is not a function of the evaporation rate. It is a complex combination of processes that are connected to both the evaporation rate AND the precipitation rate.

Renno, Emanuel, and Stone:

Clouds with high precipitation efficiency produce cold and dry climates. Clouds with low precipitation efficiency lead to moist and warm climates.

Has anyone evidence of a mechanism* which might be reducing the precipitation efficiency of the global weather systems and hence be causing warming? The process seems very delicate — perhaps something is disrupting the historical Weber number of the cloud droplets. Or maybe the CCN numbers are down. If so, I’d expect relative humidity to be going up. I’m sure I’ve seen an article about anomalous pan evaporation rates in… maybe Australia.

Julian:
I don’t know of anyone researching this…partly because most researchers don’t know about (or don’t appreciate the importance of) the issue, and also because we probably don’t have enough measurements to investigate the issue!

Well, I take that back…we found evidence of increased precipitation efficiency associated with warming of the tropical troposphere, published August 9, 2007 in GRL:

…and I am continuing this work by looking at the passive microwave signatures of precipitation systems using the AMSR-E data from NASA’s Aqua satellite (I’m the Science Team leader on that instrument). I can already report that the decrease in cirrus cloudiness with warming that we documented is also seen in the precipitation-size ice water contents of tropical thunderstorm anvils (in the 89 GHz channel of the AMSR-E). This supports the view that precipitation efficiency is tightly coupled to cirrus cloud LW feedbacks…at least in the tropics.

Thanks for the reference — beyond me, I’m afraid, as I’m looking for a basic signal, preferably a SW-reflecting cloud change, in the boundary layer, which might hint at a large effect from a small input, necessary if we are to put the A into AGW.

Your website, BTW, should be required reading for all policy makers, a simply-expressed, clear-eyed view of what is going on. It could usefully come with a large red Don’t Panic sign on the cover. One thing: the graph of twentieth century warming/cooling looks as if it had used a temperature series with the Folland and Parker adjustment. Without that adjustment — which our host here has convinced me is dubious at best — and using SSTs, the post WWII trend to ’76 is slightly upwards and, to me, looks as if the trend were ‘trying’ to get back to its natural .13 deg/decade slope.

However, I am not trustworthy on the F&P: I have my own reasons for wishing it to be false.